Stimulus-induced gamma activity in the electrocorticogram of freely moving rats: The neuronal signature of novelty detection

To investigate the cortical activity pattern associated with the exploration and identification of a novel object we recorded the intracranial electrocorticogram (ECoG) in the barrel cortex of freely moving adult rats using wireless technology. We report here that the exploration and detection of a novel object correlate with a transient increase of synchronized oscillatory activity in the 40-47 Hz frequency band. This specific cortical activity pattern occurs 200-300 ms after the first sensory contact with the novel stimulus and decreases in power in the subsequent recording sessions with the same object. During the first explorative session the increase in 40-47 Hz is associated with a simultaneous decrease in the 30-37 Hz band, which increased to a stable level already after one session. Our results indicate that synchronized gamma activities in primary sensory cortex may represent the neuronal signature for the detection of a novel object.